Press Release

BOTHELL, Wash.--(BUSINESS WIRE)--Oct. 23, 2012--
Seattle
Genetics, Inc. (Nasdaq:SGEN) today announced that it has expanded
its antibody-drug conjugate (ADC) collaboration with Abbott (NYSE:ABT).
Under the expanded deal, Abbott will pay an upfront fee of $25 million
for rights to utilize Seattle Genetics’ auristatin-based ADC technology
with antibodies to additional oncology targets. In addition, Seattle
Genetics may receive up to $220 million in potential milestone payments
per additional target upon achieving predetermined development and
commercial objectives, as well as mid-to-high single-digit royalties on
worldwide net sales of any resulting products under the multi-target
collaboration.

“ADCs have emerged as an important therapeutic approach to cancer,
driven by the FDA approval of ADCETRIS®, and encouraging data
from numerous clinical and preclinical ADC programs in development by
Seattle Genetics and our collaborators,” said Natasha Hernday, Vice
President, Corporate Development at Seattle Genetics. “We are leading
the field in ADC development, and this expanded collaboration with
Abbott further validates our technology and approach in targeting and
treating cancer.”

Seattle Genetics and Abbott originally entered into an ADC collaboration
in March 2011 under which Abbott paid an upfront fee of $8 million for
rights to utilize Seattle Genetics’ ADC technology with antibodies to a
single oncology target. Abbott is responsible for research, product
development, manufacturing and commercialization of any ADC products
under the expanded collaboration. In addition to the upfront payment and
potential milestone payments and royalties, Seattle Genetics will
receive annual maintenance fees and research support payments for
assistance provided to Abbott under the collaboration.

ADCs are monoclonal antibodies that are designed to selectively deliver
cytotoxic agents to tumor cells. With over a decade of experience and
knowledge in ADC innovation, Seattle Genetics has developed proprietary
technology employing synthetic cytotoxic agents, such as monomethyl
auristatin E (MMAE) and monomethyl auristatin F (MMAF), and stable
linker systems that attach these cytotoxic agents to the antibody.
Seattle Genetics’ linker systems are designed to be stable in the
bloodstream and release the potent cell-killing agent once inside
targeted cancer cells. This approach is intended to spare non-targeted
cells and thus reduce many of the toxic effects of traditional
chemotherapy while enhancing antitumor activity. ADCETRIS (brentuximab
vedotin) is the first drug approved utilizing Seattle Genetics’ ADC
technology.

About Seattle Genetics

Seattle Genetics is a biotechnology company focused on the development
and commercialization of monoclonal antibody-based therapies for the
treatment of cancer. The U.S. Food and Drug Administration granted
accelerated approval of ADCETRIS in August 2011 for two indications.
ADCETRIS is being developed in collaboration with Millennium: The Takeda
Oncology Company. In addition, Seattle Genetics has three other
clinical-stage ADC programs: SGN-75, ASG-5ME and ASG-22ME. Seattle
Genetics has collaborations for its ADC technology with a number of
leading biotechnology and pharmaceutical companies, including Abbott,
Agensys (an affiliate of Astellas), Bayer, Celldex Therapeutics, Daiichi
Sankyo, Genentech, GlaxoSmithKline, Millennium, Pfizer and Progenics, as
well as ADC co-development agreements with Agensys and Genmab. Across
Seattle Genetics’ internal and collaborator programs, there are more
than 15 ADCs in clinical development utilizing the company’s technology.
More information can be found at www.seattlegenetics.com.

Certain of the statements made in this press release are forward
looking, such as those, among others, relating to the therapeutic
potential and future clinical progress, regulatory approval and
commercial launch of products utilizing Seattle Genetics’ ADC
technology. Actual results or developments may differ materially from
those projected or implied in these forward-looking statements. Factors
that may cause such a difference include risks related to adverse
clinical results as our product candidates or our collaborators’ product
candidates move into and advance in clinical trials, risks inherent in
early stage development and failure by Seattle Genetics to secure or
maintain relationships with collaborators. More information about the
risks and uncertainties faced by Seattle Genetics is contained in the
Company’s quarterly report on Form 10-Q for the quarter ended June 30,
2012 filed with the Securities and Exchange Commission. Seattle Genetics
disclaims any intention or obligation to update or revise any
forward-looking statements, whether as a result of new information,
future events or otherwise.